(a) Field of the Invention
The invention relates to the production of recombinant proteins in animal's semen using the seminal gland as a bioreactor. Particularly, this invention relates to an expression system which comprises at least a semen-specific protein promoter operatively linked to a DNA sequence coding for a signal peptide and a desired recombinant protein product. When such a system is transgenically incorporated into an animal, the recombinant protein is expressed in the semen of the animal. This invention also relates to the transgenic animal that produces the desired recombinant product in its semen. Recombinant products produced by the expression systems and transgenically altered animals of this invention can be produced at significantly less cost than by conventional recombinant protein production techniques. There is also a potential to alter specific characteristics related to sperm viability and potential storage systems.
(b) Description of Prior Art
Recombinant DNA technology has enabled the cloning and expression of genes encoding medically and agriculturally important proteins and glycoproteins. Such products include, "for example, insulin, growth hormone, growth hormone releasing factor, somatostatin, tissue plasminogen activator, tumor necrosis factor, lipocortin, coagulation factors VIII and IX, erythropoietin, the interferons, colony stimulating factor, the interleukins and urokinase, antibodies.
Many of these important proteins, however, are large (molecular weights in excess of 30 Kd), secreted, require sulfhydryl bonds to maintain proper folding, are glycosylated and are sensitive to proteases. As a result, the recombinant production of such products in prokaryotic cells has proven to be less than satisfactory because the desired recombinant proteins are incorrectly processed, lack proper glycosylation or are improperly formed. Accordingly, resort has been had to the production of those recombinant proteins in cultured eukaryotic cells. This technique has proven to be both expensive and often unreliable due the variability of cell culture methods. For example, average yields are 10 mg of recombinant protein per liter of culture media, with the resulting cost typically for exceeding one thousand dollars per gram of recombinant protein. Accordingly, resort has been had to the production of those recombinant proteins in cultured eukaryotic cells. It is believed that the use of the genital tract as a tissue for expression overcomes, either wholly or to a satisfactory degree, this potential source of difficulty. Several examples using mammary glands of transgenic mammals as bioreactors have demonstrated their potential to produce recombinant protein products.
Harvesting from body fluids as opposed to solid tissue is desirable, because such routes, are by and large renewable, and most proteins of biomedical importance are themselves secreted into body fluids. Secretion into the bloodstream is a possible route, either from liver or B lymphocytes, but the coagulating properties of blood and the presence of biologically active peptides and antigenic molecules may prove a hindrance to subsequent downstream processing.
It would be highly desirable to be provided with a means to produce recombinant proteins in large quantities.